520 



STRATIGRAPHICAL GEOLOGY. 



from hand specimens to particularize the period. There are reasons for 

 believing the porphyritic type of gneiss may not be the very oldest rock 

 of the state, as instanced upon page 472. It was quite early remarked in 

 one of the annual reports that this porphyritic rock seemed to have been 

 thrust in between older strata. There are two areas of gneiss included 

 within the territorial area of the older mass in Bradford, Warner, and 

 Henniker. In other cases, an associated rock may be specified, though 

 not delineated upon the map. It is a matter of regret that this principal 

 area of porphyritic gneiss has been only slightly examined. Our studies 

 upon it were mostly confined to the early years of the survey, before it 

 was understood to be a stratified rock. Our observations of dip are 

 therefore scanty, and its stratigraphical relations not well worked up. 

 Then, latterly, also, the territory lay between the district being explored 

 by two of us, and hence it was neglected. 



Messrs. Whitney and Williams, in a description of the section from 

 Portsmouth to Claremont, speak thus of this rock : " Large boulders of 

 porphyritic granite are very numerous over the surface, from the West 

 Parish of Concord to the centre of Warner, where we find the rock itself 

 in place. It is a peculiar rock, having large crystals of feldspar uniformly 

 distributed through its mass ; they are often glassy, so as to furnish beau- 

 tiful and striking specimens. This bed of granite extends across the 

 state in a general N. E. and S. W. direction ; it is from eight to ten miles 

 in width, though often interrupted with veins of granite of various tex- 

 ture, often very coarse grained, and containing occasional beds of mica 

 slate. * * * This rock continues, on this sectional line, about three 

 miles west of Newbury, where it is replaced by mica slate." Final 

 Report, by Jackson, p. 51. 



In our second report a range was represented as extending from Wa- 

 terville to Jaffrey, connecting across from Danbury to New Hampton, 

 and not extending northerly from Danbury to Groton. Subsequent 

 observations showed the existence of two instead of one principal range, 

 and that no visible connection can be found between them. The inter- 

 vening Montalban schists may be underlaid deep down by a synclinal 

 basin of the older rock. The height of land in Springfield, New London, 

 and Sunapee is represented on the map as consisting of the Lake gneiss, 

 the porphyritic rock curving around it through Wilmot. I do not feel 



